refactor: extract updateNetworking() from GameHandler::update()

Move socket update, packet processing, Warden async drain, RX silence
detection, disconnect handling, and Warden gate logging into a separate
updateNetworking() method. Reduces update() from ~704 to ~591 lines.

include/game/game_handler.hpp

@@ -2314,6 +2314,7 @@ public:
      * @param deltaTime Time since last update in seconds
      */
     void update(float deltaTime);
+    void updateNetworking(float deltaTime);
 
     /**
      * Reset DBC-backed caches so they reload from new expansion data.